The present invention concerns a corrosion resistant steel. More specifically, the invention concerns a corrosion resistant steel suitable for use as the material for shafts of OA-machines such as printers.
Requisites to the material for parts of machines of indoor use, such as so-called OA-machines, are good cold workability and machinability, and further, such corrosion resistance as sufficient to endure under indoor circumstances. Recently, of the OA-machines personal computers have come into wide use, and with this, demand for printers has been increasing. The printers have plural shafts such as paper-supplier shaft and platen shafts. In order to reduce the costs for producing the printers it is necessary to reduce the costs for the shafts.
To date as the materials for the shafts of laser printers the following stainless steels have been used:
SUS420J2 (C: 0.26-0.40%, Si: up to 1.0%, Mn: up to 1.0%, P: up to 0.040%, S: up to 0.040%, Cr: 12.0-14.0%, the balance being substantially Fe), and
SUS410 (C: up to 0.15%, Si: up to 1.0%, Mn: up to 1.0%, P; up to 0.040%, S: up to 0.030%, Cr: 11.5-13.5%, the balance being substantially Fe).
On the other hand, as the shafts of inkjet printers such as color printers, those produced of the free-cutting steels mentioned below which are machined and nickel-plated have been used.
SUM24L (C: up to 0.15%, Mn: 0.85-1:15%, P: 0.040-0.090%, S: 0.26-0.35%, Pb: 0.10-0.35%, the balance being substantially Fe), and
SUM22 (C: up to 0.13%, Mn: 0.70-1.00%, P: 0.07-0.12%, S: 0.24-0.35%, the balance being substantially Fe), and
Because it is satisfactory that this kind of shafts have such corrosion resistance as to endure indoor circumstances, the above-mentioned expensive stainless steel, SUS420J2 and SUS410, are not appropriate materials from the viewpoint of cost-performance balance. In electroplating machined parts made of free-cutting steel as SUM24L it has been experienced that the quality of the products varies due to fluctuating thickness and defects in the plated metal layer, which results in lowered liability of the products. Further, it is necessary to consider, from the view to avoid environmental pollution, treatment of the waste solution occurring from electroplating. The expense for the treatment of the waste solution is getting higher, and thus, it cannot be said that the costs for producing the shafts according to the conventional technology are not important.
It should be noted that straightness is another problem common to the shafts.
In order to solve these problems the inventors have conducted research and development with the intention to provide a steel which has good machinability and straightness, sufficient corrosion-resistance to endure under the indoor circumstances, and further, is not expensive. As the result, they have discovered that addition of certain amounts of one or both of S and Se, and one or both of Ti and Zr to the steel containing C: 0.005-0.200%, Si: up to 1.0%, Mn: up to 2.0%, P: up to 0.05%, Cu: up to 2.0%, Ni: up to 2.0%, Cr: 2.0-9.0%, the balance being substantially Fe, results in formation of Ti-based compounds, Zr-based compounds or Tixe2x80x94Zr-based compounds containing C and one or two of S and Se such as (Ti,Zr)4(S,Se)2C2 in the steel, and that fine dispersion of these compounds in the steel improves machinability of the steel and brings about good corrosion resistance, cold workability and hot workability of the steel.
The object of the present invention is to utilize the above discovery by the inventors and to provide a steel which has good machinability and straightness, sufficient corrosion-resistance to endure under the indoor circumstances, and is less expensive.